Eldergleam Sanctuary is a dungeon in The Elder Scrolls V: Skyrim
Head into the cave and begin exploring. Inside you will find Sond and Asta. They will warn you not to harm the tree itself but also explain that no one has gotten close to the tree in a long time. Head deeper inside the area and equip Nettlebane. Approach the roots that are blocking your way forward and swing Nettlebane at them. The roots will move and clear the path forward. Follow it on forward and up to the tree itself. Head up the slope slowly to make sure that Maurice stays with you and will approach the tree with you.
At the top you will have a choice to make. This is only available if Maurice Jondrelle has accompanied you this far into the quest. At the top, he will want to talk to you. Let him and either you can attack the tree to get the sap or let him pray at the tree and you will receive a sapling. Attacking the tree will cause Maurice to become hostile and you will need to fight at least 4 [[Skyrim: Spriggan|
Let him approach the tree and he will pray to the Eldergleam. This will give you the Eldergleam Sapling.